Thermostats



JulyT 16, 1.957 w. F. sTuMP a THERMOSTATS Filed oct. 28. 1955 www INVENTOR.

TTA/x tes Patent 2,799,743 Patented July 16, 1957 ,799,7"48`"rurali/tueurs Wilbur F. Stump, Gslo Township, Elkhart County, Ind.

Application October 28, 1955, Serial No. 543,432

'.ltl Claims. (Cl. 20G-137) This invention relates to improvements inthermostats, and more particularly to thermostats of the immersion typeintended for controlling the temperature of liquid-s, such aselectroplating solutions and other corrosive baths.

The primary object of this invention is to provide a thermostat of theimmersion type having a temperature responsive element exposed to theliquid which possesses 'a high coellicient of thermal expansion and iscapable of withstanding corrosive iniluences.

A further object is to provide a device of this character which has acompensating spring therein to accommodate a wide range of temperaturevibrations without destroying the calibration of the device orendangering breakage of the device due to constriction during coldweather, land which at the same time has a high degree of sensitivity innormal operation, so that it responds to small temperature variationsduring normal use.

. A further object is to provide a thermostat employing a. thermoplastictube having a high coetiicient of expansion as a thermally sensitiveelement, and to locate and mount said tube in the device for directcontact with the liquid whose temperature is to be sensed in order toobtain maximum temperature sensitivity while at the same time avoidingthe danger of corrosion of the device by corrosive liquids constitutingthe bath and avoiding electrical conduction to metal parts of the devicefrom the bath, such as an electroplating bath, in which electricalcurrent flows.

Other objects will be apparent from the following specication.

In the drawing:

Fig. 1 is a longitudinal sectional view taken on line 1 1 of Fig. 2;

Fig. 2 is an end view of the device as viewed from the left in Fig. 1,with caps 19 and 39 removed; and

Fig. 3 is a fragmentary axial sectional view illustrating a modifiedembodiment of the invention.

Referring to the drawing, and particularly to Figs. l and 2 whichillustrate one embodiment of the invention, the numeral designates ahousing having a removable cover plate 12 mounted th'ereon and Securedthereto by means of screws or other securing means 14. The housing hasan opening 16 defined partially by a projecting neck 18, which may beclosed by a cap or bushing 19, and which provides for passage of one ormore electrical conductors 20 into the chamber or cavity 22 of thedevice.

A micro switch 24 is mounted within housing 10 and is preferably pivotedeccentrically thereof by the pivot pin 26, so that the portion thereofadjacent to the plunger or actuator 28 thereof is free to swing bodily.The micro switch 24 may be of any suitable type or constructionsusceptible of quick throw between open circuit position and closedcircuit position in response to a minute amount of movement of theplunger of actuator 28 thereof. Any suitable means may be provided foradjusting the position ofthe micro switch 24 within the housing 10.Thus, as here shown, a spring 30 is secured at 32 to the housing 10 andbears against the casing of the micro switch at one side of and spacedfrom the pivot axis 26, andthe opposite side of the micro switch casingis engaged by 'a screw 34, screw-threaded within an opening in thehousing 10, as in the cover 12 of that housing. A lock nut 36 may beprovided to maintain the adjustment of the screw as desired, .and thehead 38 of the screw will extend exteriorly of the housing to be readilyadjustable. A removable cap 39 may enclose the portion of the screwexterior of housing 10. Thus it will be apparent that 4adjustment of thescrew 34 will alter the pivotal position of the micro switch within thehousing 10.

A collar or tubular projection 40 extends outwardly from the housing 1 0in concentric relation to housing aperture 42 which confronts and isaligned with the micro switch plunger 28. An elongated rigid tube 44,preferably having a high coeliicient of expansion, is mounted in thecollar or sleeve 40, as by a pressed or threaded tit. For thisv purposethe bore of the collar 4) may be tapered and can be serrated, toothed orotherwise formed so that a rm securing anchorage of the parts can beobtained. The tube 44 is of any length desired, and preferably of alength of twelve inches or more.

The tube 44 is formed of a rigid material having a high coetcient ofexpansion. One such material is Saran, a thermoplastic resin produced bythe polymerization of the vinylidene chloride. Another polyvinylchloride material which is well suited for this purpose is known in thetrade as Uscolite These two materials have coeliicients of expansionVmany times greater than the coetiicient of expansion of stainless steeland possess the properties of resistance to corrosion in said electricalinsulation, and in `general possess all properties necessary for use inthe present thermostat construction. It will be understood that anyother material, such as other thermoplastic resins which possess theproperties aforementioned, may also be employed, and that the housing 10may be formed of such a material or of metal. A cap 46, preferablyformed of thermoplastic material having the aforementioned properties islixedly mounted -upon the outer end of the tube 44, as byscrew-threading or bonding thereof. A plug or plate 48 seats within thecap 46, and a washer 50 may be interposed between the same and the endof tube 44'for the purpose of insuring an effective yseal of the tubeend.

A spacer sleeve 52 tits within the tube 44, and has an annular ange 54pressed against the wall of housing 10 by theend of the tube 44. Thesleeve or collar 52 serves las a means to mount or support within thetube 44 one end of an elongated tube 56 which extends for the majorportion of the length of the tube 44. Tube 56 serves to impart strengthand rigidity to said tube 44 and to guide the movement of the switchactuator to be described hereinafter. Tube 56 is preferably formed ofmetal and is concentric with the housing opening 42.

`An elongated'rod 58 of metal or other thermally expansive rigidmaterial, but having a different coeicient of expansion than that of thetube 44, is located within the tubes 44 and 56. Rod 58 is iixedlyanchored at one end upon plate or plug 48, as by soldering orscrewthreading thereof to the plug. Rod 58 extends in centered relationto the tubes 44 and 56, with substantial clearance in the tube 56. Therod 58 is of a length shorter than the length of the tube 44, so as toterminate spaced from the casing 10. A head 60 is mounted upon the inneror left-hand end of the rod 58 as viewed in Fig. l, said head preferablyincluding a skirt portion 62 surrounding a portion of therod 58. Thediameter of the head 60 and skirt 62 is preferably uniform externally,and is less than the diameter of the bore of the tube 56.

A tubev 64 hasv a snug sliding tit within the tube 56,

and also has a snug slidingr tit around the head 60. One end of tube 64has an inturned flange 66 which bears against the inner or right-handend of the head 60, 62, as seen in Fig. 1. The other endof the tube 64mounts a head or end member 68 which closes the tube 64 and servestoretain therein an elongated coil spring 70 whoseA opposite ends bearagainst the head of rod'58, and the.

end or cap member 68 of the tube 64. The force ofthe spring 70 exceedsthe force of the spring (not shown) which presses outwardly the plunger28 of the micro switch 24, so that movement of the rod 58 in a directionto trip the plunger 28 of the micro switch will. be effective for thatpurpose after initial contact has been established between the endmember 68 and the switch plunger 28. However, if this movement of therod 58 continues after the switch plunger 28 has been actuated, and inparticular after end member 68 engages a fixed part of the micro switch,the spring 70 will yield to accommodate lost motion of the parts, i. e.,sliding of the head 60 within the tube 64 and away from the flange 66 oftube 64.

In the preferred form of the invention, where the tube 44 is of a highlyexpansive material and the rod 58 is of a material of lesser expansiveproperties, it will be apparent that the use of spring 70 willcompensate for contraction of the tube 44 when the device is subjectedto a temperature condition substantially below that for which it hasbeen calibrated. Thus, the device can be calibrated accurately at thefactory for a given temperature range or setting, and then can beshipped in cold weather, i. e., subjected to temperatures much lowerthan the critical or switch-actuating temperature for which the devicehas been set, without danger of breakage due to great contraction of thetube 44 compared to that of rod 58. The same condition olers the furtheradvantage that the thermostat will not be subject to injury or darnageof calibration in the event the temperature thereof is not maintainedconstant during periods when the device is not in use, as during periodsof shut-down of a factory or the like. This is of great importanceinasmuch as the usual micro switch constructions do not provide means totake up a substantial amount of over-travel. Thus, conventional microswitches dol not accommodate a long stroke or throw of an actuator and,particularly, do not have a range great enough when used in a thermostatto take up the contractions occurring upon substantial temperaturechanges within elongated temperature sensitive members, such as a tube444 yformed of a material having a high coefficient of expansion and ofsubstantial length, for example, lengths of from twelve to thirtyinches, or even more. Therefore, by virtue of the lost motion of theswitch actuating device andthe use of the spring 70, the present devicesecures the advantages of great temperature sensitivity due to itselongated thermally expansible parts, and the great accuracy andsensitivity to small motions which characterize a micro switch, withoutendangering the micro switch when the temperature range for which thedevice is set exceeded substantially, as during freezing weather or insubfreezing atmospheres.

One of the important characteristics of the device is the fact that thetemperature sensitive tube 44 is in direct contact with the liquid whosetemperature is to be controlled. This results in obtaining maximumtemperature sensitivity in the device. The use of plastic material forthe tube 44 and the endcap 46 and other parts permits direct contactthereof with acids and other corrosive liquids, and also insures againstelectrical 'conduction of currents from the liquid to the metal parts ofthe device, such as the metal rod 58, the tube 5,6, and associatedparts. The device is thus particularly suited for use in electroplating,and in other acidic'solutions, and particularly for liquids operating attemperatures in a range below the softening point of the thermoplastic.In this connection, electroplating solutions commonly operate attemperatures between 120 F. and 140 F., and thermoplastic material iseffective for its intended purpose at that temperature range. Theoperating range of the instrument is approximately from 60 F. to 170 F.or more. The temperature setting of the device is readily controlled byadjustment of the screw 34 to locate the micro switch 24, so that thelatter will operate at the critical temperature selected or desired.

Because of the high coeicient of expansion of the thermoplastic tube 44compared to that of the rod 58, and because of the sensitivity of themicro switch, it is possible to control the temperature of a liquid veryaccurately. Thus, in cases where the tube is submerged in a liquid to adepth of approximately eighteen inches, it is possible by thisconstruction to operate the device with a fixed or maximum differentialof about 1 F.

The micro switch 24 may be either of the single throw type of the doublethrow type. Where a micro switch of the double throw type is'employed,the thermostat can bezused for either heating or cooling applications,that is, to control the liquid to prevent heating thereof above apredetermined point or oppositely to control the liquid to preventcooling thereof below a predetermined temperature.

To the best of my knowledge no thermostat has been available for use inacidic or electroplating solutions heretofore. Instead,.temperatureresponsive valve controllers have. been employed, the same being of thetype requiring a capillary pressure responsive element, such as aSylphonbellows and a connected capillary tube and bulb. The Sylphonbellows or other pressure responsive elementsusnally are formed of metaland, therefore, it has beenY .necessary that acid contacting partsthereof be coated or sheathed in lead. VThis has resulted in a lowsens'itiyity iof prior constructions, so that differential temperatureshave existed in the order of about 5 F. Applicants. device Yemploying athermoplastic tube 44 thirty inches in length', immersed for eighteeninches and employing avmicro switchresponsive to a pressure ofapproximately one and one-half ounces, has operated satisfactorily witha-diferential temperature operation of approximately 1 F.

In the modified form of the invention illustrated 1n Fig. 3, partssimilar-to those in Figs. l and 2 bear the same reference numerals. Inthis construction, the micro switch 24 is inverted from the position ofFig. l, so that its pivot axis 26' is located adjacent to and insubstantial alignment with the head 68 mounted on the tube 64 carried bythe rod 58. Thefplunger or sensing member 28' of the micro switch islocated remote from the head 68', and the adjusting screw 34 is locatedsubstantially in alignment with the feeler 28' of the micro switch. Inthis construction a lever is pivoted at 82 to the housing 10 adjacent tothe head 68'. The free end of the lever may include a contact portion84, such as a rounded head, adapted to contact the micro switch feeleror plunger 28. The spacing between the pivot axis 82 and the point ofcontact with the member 68 will be much less than the spacing betweenthe point of contact with the member 68 with the lever 80 and the pointof contact of the lever end 84 with the switch part 28.

By this construction it is possible to secure, in the thermostat havingthermally sensitive elements 0fv comparatively short length, asensitivity comparable to that of a device employing elements of muchgreater length. Thus, the lever 80 serves to multiply the movementproduced by or occurring at the tip of the member 68'. Hence, it ispossible to operate the device at a very low temperature differential incases where the physical travel of the member 68 during such temperaturedifferential is too small to normally operate the micro switch. Observein this construction also that the spring 30 can be omitted if desired,it being understood that the spring 30 may also be omitted from the Fig.l construction if desired.

While the preferred embodiments of the invention have been illustratedand described, it will be understood that changes in the constructionmay be made within the scone of the appended claims Without departingfrom the spirit of the invention.

I claim:

1. A thermostat adapted to be immersed in liquid, comprising a housing,an elongated expansible tube secured to said housing, means sealing theouter end of said tube, an elongated member anchored to the tubeadjacent to its outer end and extending therethrough with clearance andinto said housing, said member including an elongated compressible coilspring, means for positioning said member relative to said tube saidmember and tube having different coefficients of expansion, amicroswitch pivoted in said housing and having an actuating part remotefrom said pivot axis and engaged by said member, and means forpositioning said microswitch in said housing.

2. A thermostat as defined in claim 1, wherein said tube is formed of athermoplastic material having a high coeiiicient of expansion andcapable of resisting corrosion by acid. y

3. A thermostat as defined in claim 1, wherein said elongated memberincludes a pair of spring pressed parts having a lost motion connection.

4. A thermostat of the immersion type comprising a housing, a microswitch pivoted in said housing and including an actuator part remotefrom its pivot, an adjustable stop for limiting pivoting of said microswitch in said housing in one direction, and a pair of outer and innerelongated members interlitting with clearance and having differentcoefficients of expansion, means for positioning said members inselected relation, the outer member being fixed to said housing, andbeing sealed to prevent entry of liquid therein, and the inner memberhaving a part anchored to the outer free end of the outer member and asecond part shiftable relative to said anchored part and an elongatedcoil spring pressing said second part to a limit position relative tosaid anchored part, said second part engaging said actuator part tonormally press said micro switch against said stop.

5. A thermostat as defined in claim 4, and a spring pressed contactmember carried by the free end 0f said inner part and engaging saidactuator part.

6. A thermostat as defined in claim 4 wherein said inner membercomprises a rod having a head at its free end, a tube slidablyencircling said head, stop means on said tube engaging said head tolimit sliding of said tube on said head in one direction, a coil springin said tube, and a contact member carried by said tube, said contactmember being engaged by said spring and pressed against said actuatorpart.

7. A thermostat as defined in claim 6, and a guide for said tube carriedby said housing.

8. A thermostat as defined in claim 4, wherein said outer member isformed of a thermoplastic resin having a higher coefficient of expansionthan said inner member.

9. A thermostat as defined in claim 4, wherein said housing and outermember are both formed of acid resisting thermoplastic resin material.

10. A thermostat as defined in claim 4, and a spring carried by saidhousing and engaging said micro switch opposite said adjustable stop.

References Cited in the file of this patent UNITED STATES PATENTS2,498,988 Eden et al. Feb. 28, 195() 2,705,746 Strange Apr. 5, 1955FOREIGN PATENTS 715,922 Great Britain Sept. 22, 1954

